Hotrod Build Thread

[guavatone]

Really bad sign. I hope you have a fuse in there!

Sorry you don't seem to be getting consistent advise. different people are hooking the up differently depending on PSU or just preferences. I am still trying to figure the best way to hook mune up so sorry if I have messed u up.

 

[bluezplaya]

Gentlemen, ahem...

http://www.groupdiy.com/index.php?topic=281705#281705

:guinness:

 

[madriaanse]

Again, nice work Adam!!

you wrote:
"Yes, it is getting 24+ and 48+ properly when not hooked up to the Neves. I don't know if the VRegs are heatsinked. How do I do that? "

What I've started doing is extending the leads of the LM317s with wire and 'remote mounting' them on a big 30-50W TO-3 heatsink. Overkill I know, but they stay cooler this way and that can't hurt. Mounting them away from the PCB also keeps the heat off the other components surrounding Vreg. If I remember correctly (don't quote me on this), two channels of 1290 will have the Vreg dissipating around 17W in heat. So if you don't heatsink well the Vregs get HOT, greatly shortening the life span of the component and possibly the parts surrounding it.

I've also had good luck mounting the LM317's to a cast aluminum enclosure. The thermal conductivity of the aluminum combined with the large size of the case seems to make for a fine heatsink.

All the best,

M.

 

[guavatone]

Has anyone had trouble with these alpha switches or am I just lucky. I noticed that the one in my circuit had differences in my unsoldered one. 1st I saw that the rotating waver was farther ftom the contacts and 2nd the post in the middle was slightly more recessed.


Anyone have another 12P 2 deck switch they like? I really don't need this headache. what a PITA

 

[madriaanse]

http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=GH7103-ND

But I prefer:

http://www.elma.com/Admin/ProductionFiles1/ProductTypeFile/371/English/Type_04.pdf

M.

 

[guavatone]

M, is that digikey 2 Poles and 12 positions?

The info on that is very misleading. I was looking at it and it says 1P :?

I was about to call them to make me a custom switch

 

[madriaanse]

Hi Guava,

It's really a 2 pole -> 1 pole/deck, 2 decks = 2 pole

The grayhill code also spells this out:
71BD30-02-1-AJN means: a Series 71 switch with a 1/4" shaft, adjustable stop, 30deg throw (12 pos), 2 decks, 1 pole per deck

Later,

M.

 

[guavatone]

Thanks M. Last question. Does a shorting switch make a difference with clicking between positions.

BTW Allied has em for a buck less

 

[madriaanse]

I'd go for the non-shorting. They're quieter to switch.

M.

 

[dissonantstring]

[quote author="madriaanse"]I'd go for the non-shorting. They're quieter to switch.

M.[/quote]

hi madriaanse,
is this true? i've always opted for shorting when using a switch for gain attenuation. seems against logic because the contact is broken when switching between positions with a non-shorting (BBM) switch. it may just be the circuit it's implemented in though and i'm a newb so i can't definitively say which is correct. i have seen non-shorting switches used in gain control before though (as in Chae's Bellerophon mic pre).
i'm sure you're speaking from experience though.
regards,
grant

 

[madriaanse]

Yeah I've had better luck with non-shorting switches - especially on 1073/1290 pre's when you switch in the 2nd pre stage. There is a small click when switching the 5db steps, but nothing huge. Having a stop (break) before the 2nd pre stage switches in is nice.

M.

 

[dissonantstring]

thanks for the info M.
hmmm, i dont' think the HR board has the bump in the second gain stage like a 1290 attenuation set up so not sure if it will help having it in the HR circuit.
need to study up on this. thanks again for the insight.
cheers,
grant

 

[guavatone]

Here is thread I found last night. But nothing conclusive. Maybe I'll leave my alpha together and wire the greyhills to A-B for kicks.

http://www.groupdiy.com/index.php?topic=237269&highlight=1272+nonshorting#237269

 

[Greg]

The first deck of the gain switch is an attenuator.

The second deck of the gain switch controls the gain of the first stage.

The 5K output pot is between stages.

The second stage is fixed at 15dB gain.

No third gain stage.

 

[dissonantstring]

great info! thanks greg!

 

[bluezplaya]

Okay I have been enjoying my new 1272's but I seem to be having a problem with resistors burning up. One of my channels had some sort of funky hum to it when the input switch was half way up and the output pot was about the same. If I moved the OP volume all the way up or all the way down the noise went away. So I turned the trimpot on the 283 card while listening until it went away. I know that's obviously a bad idea because according to Joe Malone, that controls the amount of current going through board. My DMM doesn't read current so I just listened. But now obviously there is too much current because the R7 is burnt up.

 

[Greg]

Yes, some you have to be careful with the trimmer. I like the current method, but some people adjust for symmetrical clipping. Works well.

 

[bluezplaya]

Greg, the 47 ohm resistor on the 283 card of one of my channels continually gets burnt up. How can i fix that??

Adam

 

[Greg]

Have you set the bias with the trimpot?

 

[bluezplaya]

How do I "correctly" do that?